(ESH) Miocene Concentrations and 13C of Atmospheric Carbon Dioxide Inferred from Stomatal Density and 13C of Fossil Leaves

9510078马歇尔稳定碳同位素比率和中新世叶片的气孔特征将与现代近亲(NLR)的叶片进行比较。NLR的植物标本将被分析，以校准自工业革命以来大气二氧化碳浓度增加30%和同位素组成减少1.2%的情况下的同位素组成和气孔特征。利用校准，我们将从化石数据中获得10到20个独立的、特定于分类群的对中新世大气中二氧化碳的同位素组成和浓度的估计。这些树叶化石是1500万年前在爱达荷州克拉基亚市附近的缺氧湖沉积物中发现的亚热带和温带树木。植物区系中的优势树种有栎属、板栗属、水杉属、红豆杉属等。这些保存完好的化石之前已经产生了DNA，分类群特有的类黄酮类成分，有时当第一次从沉积物中移除时，仍然是有色的。据我们所知，它们是这个时代世界上保存最完好的标本。然而，为了最大限度地减少成岩作用对同位素组成的影响，所有的比较都将依赖于从现代树叶和化石中提取的木质素。气孔密度(每平方米叶表面的气孔数)和气孔大小将在所有叶片的重复样本上测量；气孔指数(#气孔/(#气孔+表皮细胞))将在可能的情况下测量。还将收集最接近的在世亲属的新数据，以量化树冠位置和海拔高度的影响。中新世中期是气温和二氧化碳浓度迅速下降的时期。已发表的对大气成分的估计依赖于来自海洋沉积物的同位素数据，这些数据是不确定的，因为它们距离大气几步之遥。我们提出了一种基于陆地植物的重建大气成分的替代方法，这些植物与大气更好地耦合。由于单独的属可以单独分析，这项工作将提供每个属的大气成分的独立估计。如果成功，这项工作可能最终导致对中新世陆地光合作用的分析，这是从大气中去除二氧化碳的主要生物地球化学过程之一，并可能限制我们对陆地生态系统对大气中二氧化碳持续增加的反应的估计。

9510078 Marshall Stable carbon isotope ratios and stomatal characters of Miocene leaves will be compared to those of modern leaves from nearest living relatives (NLR) Herbarium specimens of the NLR's will be analyzed to calibrate isotopic composition and stomatal characters against the 30% increase in atmospheric carbon dioxide concentration and the 1.2% decrease in isotopic composition since the industrial revolution. Using the calibrations, we will obtain from the fossil data ten to twenty independent, taxon-specific estimates of the isotopic composition and concentration of carbon dioxide in the Miocene atmosphere. The fossil leaves are of subtropical and temperate trees deposited ca. 15 million years ago in anoxic lake sediments near clarkia, Idaho. The dominant trees in the flora included species of Quercus, Castanea, Pseudofagus, Metasequoia , and Taxodium. These remarkably preserved fossils have previously yielded DNA, taxon-specific flavonoid profiles, and are sometimes still pigmented when first removed from the sediments. They are, to our knowledge, the best preserved specimens of this age in the world. Nonetheless to minimize the influence of diagenesis on isotopic composition all comparisons will rely on lignin extracted from the modern leaves and the fossils. Stomatal density (# stomata per m2 of leaf surface) and stomatal size will be measured on replicate samples of all leaves; stomatal index (#stomata/(#stomata + epidermal cells)) will be measured where possible. New collections of the nearest living relatives will also be made to quantify the effects of canopy position and altitude above sea level. The middle Miocene was a time of rapidly falling temperatures and CO2 concentrations. Published estimates of atmospheric composition rely on isotopic data from ocean sediments, which are uncertain because they are several steps removed from the atmosphere. We propose an alternative means of reconstructing atmospheric composition based on land plants, which are better coupled to the atmosphere. Because individual genera can be analyzed separately, the work will provide an independent estimate of atmospheric composition from each genus. If successful, this work may eventually lead to analyses of Miocene terrestrial photosynthesis, one of the major biogeochemical processes removing CO2 from the atmosphere, and may constrain our estimates of terrestrial ecosystem responses to the ongoing increase in atmospheric CO2.